I work in DC, so DC and / or Federal law would also be relevant. I believe the distracted driving statutes in DC would also apply to bikes, so headphones would fall under that I believe.

DC, VA, and MD also have contributory negligence. You can read more about that here:

http://greatergreaterwashington.org/post/24312/what-is-contr...

TL;DR you can receive no damages if you break the law in any tiny way while on a bicycle or on foot. Wearing headphones might be said to have contributed in some way, so you might get nothing.